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Antonia Warner
Robyn Lesh
Margaret Coad
2.002 Lab M3­5
Due: 5/9/2014
Directionality and Strength in 3D Printed Specimens
I. Introduction:
3D Printing is a manufacturing technology that has gained much popularity in the past 25
years. Since its invention in the late 1980’s, it was primarily used as an industrial tool, but
starting in 2007, 3D printers became available to the consumer market, and the total amount of
sales has snowballed since then, as shown in Figure 1.
Figure 1: Cost of 3D printers sold per year from 1988 to 2011. Sales of consumer­grade
machines began in 2007 and outpaced sales of industrial­grade machines in 2011.
3D printing is unique as a manufacturing method in that its central principle is building a
component layer by layer from a 3D model. This is in contrast to machining, which is removing
material from a piece to reveal the finished part. Some advantages of 3D printing are its
flexibility, its lack of dependence on manufacturing tools, and its ability to quickly make a part
that’s never been made before. With 3D printing, parts can be made that could not be
manufactured before, such as spheres inside spheres. Any shape that you can dream of can be
3D printed, as long as you have a 3D CAD model of it. Also, with 3D printing, you do not need to
modify your design based on limitations in the manufacturing process, as so often happens with
machined parts. 3D printing allows truly design­driven manufacturing, as opposed to
manufacturing­driven design. Finally, with 3D printing, an entirely new part can be printed in the
same amount of time as a part that has been made before, as no molds are needed. This
allows easy and quick prototyping and innovation.
As 3D printing gains popularity, there becomes a higher and higher demand for 3D
printed parts to be used in structural components, where their mechanical strength is important.
For example, Made In Space is a company founded in 2010 with the goal of making 3D printers

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capable of printing in a zero­gravity environment so that they can be brought aboard spaceships
and space stations. These 3D printers in space could be used to print emergency repair parts
for any structural component that might fail in space. In applications like this, understanding the
strength properties of 3D printed parts is crucial, and that is what we hoped to accomplish in this
project.
Our goal was to measure the strength of 3D printed parts, in both bending and tension tests,
with a focus on comparing strengths of parts printed in different print layer orientations. The fact
that 3D printed parts are made in layers was the most interesting variable to us, and the one that
we expected would most affect the mechanical properties of 3D printed parts.
II. Background:
Fused Deposition Modeling
3D printed parts are made in four common ways: Stereolithography (SLA), Selective Laser
Sintering (SLS), 3D Printing, and Fused Deposition Modeling (FDM). SLA works by converting
liquid resins into solids layer­by­layer using light. SLS fuses powdered material together using a
laser or electron beam. 3D Printing cures powdered material by local deposition of a binder.
FDM extrudes heated thermoplastic material and deposits it directly on on the previous layer,
where it solidifies immediately.
Fused deposition modeling is the most commonly used method of 3D printing. In contrast to the
other methods, it uses production­grade thermoplastics, which makes its parts chemical and
thermal change resistant, and mechanically strong. Thermoplastic, most commonly ABS, is
heated above its melting temperature and extruded through a small hole in the printhead. The
printhead moves in x and y to create the pattern required in each horizontal layer, and once the
layer is complete, the table holding the part moves down one level so that a new layer can be
printed directly on top of the other layers. The entire chamber is kept at a temperature of
approximately 200°F, just below the melting temperature of the plastic. This temperature is high
enough so that the layers don’t cool too quickly to be able to stick together, but low enough so
that the whole piece does not melt. together
Three Point Bending Tests
In this experiment, we used three­point bending tests to determine the mechanical strength
properties of our 3D printed samples. A typical three­point bending test uses a small beam with
a square cross­section, whose length is at least eight times its width, so that beam bending
equations apply. Figure 2 shows a diagram of the typical setup.

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Figure 2: Typical three­point bending test setup. A force is applied in the center of the beam,
which is supported at its two ends. The applied force and the deflection at the center of the
beam are measured.
The force and displacement at the center of the beam are typically measured and plotted against
each other, as shown in Figure 3.
Figure 3: Force versus displacement at the center of the beam in three point bending. The
structural stiffness K and the yield force Fe can be read from the graph.
From the force versus displacement curve, the values of structural stiffness K (the slope of the
linear region) and yield force Fe (the force at which the curve ceases to be linear) can be taken.
Using beam bending equations, these numbers can used to calculate the beam material’s
Young’s modulus E and yield stress σy, from the following equations.
σy =Fe*L*h/(8I), and E = K*L^3/(48I).
Tension Tests
We also used tension tests to determine the mechanical properties of our specimens. In a
typical tension test, a dog bone­shaped specimen is made out of the desired material, and the
specimen is gripped in the thick region on both ends and pulled apart. The dog bone shape is
typically used because the grips create extra stress in the material, which would cause failure at
the grips almost every time if the specimen were of uniform cross section. The cross section is

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made larger at the grip location so that the stress at that location is less than the stress in the
middle of the piece. Typically, cross sectional areas should be at least four times larger at the
grip location than in the center of the piece. Figure 4 shows a typical tension test setup.
Figure 4: Typical tension test setup. Specimen is gripped at both ends and pulled apart. Force
and displacement between the two grips are measured.
Force and displacement between the two grips is measured and used to create an engineering
stress versus engineering strain graph, as shown in Figure 5.
Figure 5: Typical stress versus strain graph for a tension test.
From the stress versus strain graph, the values of yield stress σy (the stress at which the curve
ceases to be linear) and Young’s Modulus E (the slope of the curve in the elastic region) can be
taken.

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III. Experimental Design:
Our Printer
Figure 6 shows the 3D printer that we used to print all of our specimens. It is a Dimension BST
1200es printer made by Stratasys, the company that holds the patent for Fused Deposition
Modeling.
Figure 6: The Dimension BST 1200es printer.
The options available on the printer were two different layer resolutions and three different
internal fill patterns. We chose the finest layer resolution, which meant that the height of each
layer in the z­direction was 0.01 in.
The three different internal fill patterns available were solid, high density, and low density. For
most of our samples, we chose the low density fill pattern in order to save printing time, material,
and cost. For one sample for bending and one sample for tension, we chose the solid fill density
so as to provide a control. Figure 7 shows examples of what the two fill densities that we chose
look like side by side.
Figure 7: Upper sample is a cross­section of a beam printed with low density fill. Lower sample
is a cross­section of a beam printed with solid fill.

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Our Test Apparatus
Figures 8 and 9 show our test apparatuses for the bending and tension tests. For bending, the
deflection at the center of each beam was increased at a rate of 0.05 mm/s, and the resulting
force was measured using the computer attached to the Instron machine. For tension, the
displacement between the two grips was increased at a rate of 5 mm/min for first few
specimens and 2.5 mm/min for the rest of the specimens.
Figure 8: Bending test apparatus.
Figure 9: Tension test apparatus.
Orientations of Our Samples
Our bending specimens were square beams ⅜” x ⅜” x 3.5” long, and our tension specimens
were dog bones with a thin middle section of diameter ⅜” and height 1.25”, and thick sections on
the end of height 0.5” and diameter 1” cut off to a thickness of ½” so that they could be gripped
by the jaws in the tension test machine.
We chose to test three different printing orientations for each type of test. We printed both our
bending beams and our tension dog bones lying down, standing up, and at a 45 degree angle.
Figure 10 shows some of our specimens as they came out of the printer.

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Figure 10: Specimens on the printer tray freshly out of the printer. Some are printed vertically,
some are printed horizontally, and the rest are at a 45 degree angle with support material holding
them up.
Figures 11 and 12 show our naming conventions for our specimens. For the bending
specimens, in addition to the three print orientations, there were two ways to orient the
horizontally printed specimens and the angled printed specimens in the test machine. This gave
us a total of five different orientations for the bending specimens and three for the tension
specimens.
Figure 11: Our naming conventions for the five bending specimens. The “vertical” and
“horizontal” specimens are printed the same way but oriented differently in the test machine.
The “angled top” and “angled side” specimens have the same relationship.
Figure 12: Our naming conventions for the three tension specimens.

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Internal Fills of Our Samples
Although in printing our samples, we specified a single internal structure for our parts, we found
that the internal structure of the pieces depended on the direction that the parts were printed. In
general, if the cross­sectional area of the layer was large, the cross­hatching was large (typically
squares of side length 4 mm), and if the cross­sectional area of the layer was small, the
cross­hatching was small (typically squares of side length 1 mm). This was not something that
we expected or that the printer allowed us to control.
For our bending specimens, the beams labeled “horizontal” and “vertical” had the large
cross­hatching shown in Figure 13, which we called “sparse”. The low density of these parts
was evident in the fact that their weight was very low: 4.87 grams compared to the 8.06 grams of
the solid control beam.
Figure 13: “Sparse” fill density, which consists of squares of side length 4 mm. “Horizontal” and
“vertical” bending specimens had this fill.
The bending beams labeled “square” had the small cross­hatching shown in Figure 14, which
we called “dense” fill. The higher density of these parts showed in their weight: 7.06 g.
Figure 14: “Dense” fill density, which consists of squares of side length 1 mm. The “square”
bending specimens had this fill.
Finally, when we cut one of the bending beams labeled “angled top” or “angled side” open, the
cross­section appeared solid, as shown in Figure 15. This was reflected by the heavy weight of
these pieces, 7.96 g, which was only 0.1 grams less than the solid horizontally printed piece. As
a result, for the sake of simplicity, we chose to approximate the angled specimens as “solid”.

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Figure 15: “Solid” fill density. The solid control specimen had this fill, as well as the “angled top”
and “angled side” specimens.
The variations in fill densities of our tension test specimens were even more unexpected. Not
only did the fill patterns vary between pieces printed in different orientations, but they also varied
within single pieces. For the “horizontal” tension piece, the entire sample had the “sparse” fill
density shown in Figure 13 above, giving it a weight of 6.42 grams. However, for the “vertical”
and “angled” tension pieces, the large­diameter end sections had the large, 4mm square,
crosshatching, while the small­diameter middle sections had the small, 1mm square,
crosshatching. This gave the “angled” specimens a weight of 6.88 grams, and the “vertical”
specimens a weight of 7.45 grams. This change within the piece is shown from various angles
in Figure 16.
Figure 16: Fill patterns for the “vertical” tension piece. LEFT: fill pattern in the small diameter
section, MIDDLE: transition between the two sections, RIGHT: fill in the large diameter section.
IV. Hypothesis:
Our hypothesis was that 3D printed pieces would be weaker between printed layers and
stronger within the layers. In other words, for our bending pieces, the more perpendicular the
layers were to the applied bending moment, the stronger the pieces would be. Thus, we
expected that the sigma_y and E values for the bending pieces would be, in order from greatest
to least:
Vertical = Horizontal > Angled Side = Angled Top > Square.
For the tension pieces, we expected that, the more parallel the layers were to the direction of the
force, the stronger the pieces. Thus, we expected that the sigma_y and E values for the tension
pieces would be, in order from greatest to least:
Horizontal > Angled > Vertical.
There are two reasons that we expected 3D printed pieces to be weaker between the printed
layers than within the layers. The first is that we expected that two strands of plastic would stick
together better if they were both warm than if one was cool and one was warm. Thus, since the
part was printed layer by layer, we expected that the extrusions within each layer would stick to

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each other better than they would stick to the previous layer below them, since the previous layer
had more time to cool.
The second reason that we expected weakness between layers was that the extrusions were
cylindrical, so at best, the area of contact for extrusions between layers was a single line along
the length of two cylinders. Instead, within layers, the extrusion itself held areas together, giving
a much larger area of contact.
V. Bending Test Results:
Below are the various applied force vs. displacement graphs generated from our eleven tests of
bending specimens in various orientations. For these specimens, we were only able to directly
compare the yield forces and spring constants for those pieces with the same internal density.
This was due to the fact that while all the parts had the same dimensions, only a couple had the
same moments of inertia.
Dense Specimen: The bending test results for the square specimens are shown in Figure 17.
Due to the fact that we only had one type of specimen that had dense fill, we were unable to
directly compare it to any other pieces.
Figure 17: Bending test results of two specimens printed vertically, termed “square” due to their
square layers. No plasticity was observed in these specimens; they were loaded elastically to an
average yield force of 271.7 N before failure. The average spring constant found in these tests
was 167.36 kN/m.
Sparse Specimens: The data from the “vertical” and “horizontal” specimens, those termed
“sparse” are shown in Figures 18 and 19. From this data, we observe that orienting layers

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vertically results in a higher spring constant and yield load than orienting layers horizontally. This
makes sense intuitively due to the relative ease in bending a beam with a larger cross sectional
area perpendicular to the direction of force application.
Figure 18: One vertical specimen was tested, instead of the intended two due to experimental
error. This test yielded a spring constant of 160.14 kN/m and a yield force of 366 N. This material
was observed to not be very hard due to the fact that it was not very resistant to plastic
deformation.
Figure 19: Three tests of horizontally printed specimens yielded an average spring constant of
140.42 kN/m and an average yield force of 273.03 N.

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Solid Specimens: The data from the solid beam and the angled pieces are shown in Figures 20,
21, and 22. For the angled pieces, we found that the spring constants and yield forces were
close to identical, showing that the orientation of a 45 degree angled plane has negligible effect
on the performance of the piece in bending. The solid horizontal piece had a much greater spring
constant and yield force than either of the angled pieces.
Figure 20: Due to the price of the solid parts, we printed only one solid beam horizontally. This
tests resulted in a spring constant of 214.19 kN/m and a yield force of 394.6 N.
Figure 21: Two tests of specimens printed at a 45 degree angle yielded an average spring
constant of 171.34 kN/m and an average yield force of 318.75 N. These angled pieces were
placed with the angle in the x­z plane with the angle visible on the side of the piece.

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Figure 22: Two tests of specimens printed at a 45 degree angle yielded an average spring
constant of 172.16 kN/m and an average yield force of 328.2 N. These angled pieces were
placed with the angle in the x­y plane so that the angle was visible on the top of the piece.
VI. Bending Test Analysis:
In order to be able to directly compare the behavior of all of the specimens subjected to
three­point bending, we had to find their material properties ­ specifically the Young’s modulus
(E) and the yield stress (σy). This was accomplished using the following equations:
By substituting in the spring constant (K) and yield force (Fe) found graphically, and the moment
of inertia (I) value for each specimen, we could obtain E and σy.
In order to find the moment of inertia for each specimen, we made a number of approximations.
For the sparsely filled pieces, we chose to approximate them as a shell with a certain wall
thickness, as shown in Figure 23.

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Figure 23: The cross section shown at the left depicts the cross­section chosen to approximate
the structure of the sparse specimens. The thickness of the top and bottom parts of the shell
was 0.0445 inches and the thickness of the left and right walls was 0.0615 inches. The cross
section at the right shows the cross section of the solid test specimens. Both cross sections
have outer dimensions of ⅜ in. by ⅛ in.
Using these cross sections and dimensions, we were able to find the moments of inertia of the
solid and sparse pieces as follows:
Ishell = (1/12) [b*h3
­ (b ­ t1)*(h ­ t2)3
]
t1 = 0.0615 in
t2 = 0.0445 in
Ishell = 4.8156 x 10­10
m4
Isolid = (1/12) b*h3
Isolid = 6.8593 x 10­10
m4
Due to the fact that the dense test piece was an irregular shape, we were unable to find an
equation to describe its moment of inertia. In order to approximate it however, we chose to use a
linear interpolation between the shell and solid moments of inertia, scaling by the masses of the
test pieces.
mshell = 4.87 g (msolid ­ mdense )/(msolid ­ mshell ) = .29
msolid = 7.96 g .29 * (Isolid ­ Ishell) = .595252 x 10­10
m4
mdense = 7.06 g Idense = Isolid ­ (.595252 x 10­10
)
Idense = 6.26405 x 10­10
m4
Having acquired these approximate moments of inertia, we were able to use the equations
shown above to generate the following table:
Beam Orientation E (GPa) σy (MPa)
Angled Top (solid) 2.3025 42.16
Angled Side (solid) 2.3135 43.41
Horizontal (solid) 2.8783 52.19

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Horizontal (shell) 2.6878 51.44
Vertical (shell) 3.0653 68.95
Square (dense) 2.4627 39.35
Our experimentally determined value for the Young’s Modulus (E) ranged from 2.3025 GPa to
3.0653 GPa (with an average of 2.618 GPa), while our yield stress value ranged from 39.35 MPa
to 68.95 MPa (with an average of 53 MPa). The given values for the Flexural Modulus and
Flexural Strength of the plastic we used were 2.25 GPa, and 53 MPa respectively. These values
were close to the range of values we found for our specimens, thereby validating the accuracy of
our test results.
From these various tests, several trends in our data became apparent. First of all, our
hypothesis for the bending yield stress was shown to be true, in that the more perpendicular the
printed layers were to the direction of force application the stronger the beam. In addition, we
found that for the horizontally printed specimens, the vertically oriented layers were stronger than
those with layers placed horizontally. From highest to lowest yield stress, the strongest
specimens were: Vertical, Horizontal, Angled, Square.
In regards to our bending elastic modulus, we found our hypothesis to be mostly validated. The
vertical layers were once again stronger than the horizontal layers, and both of these were
stronger than the square and angled layers. However, the data suggests that the square
specimens had a greater elastic modulus than the angled pieces. This is contrary to what we
had expected due to the fact that the angled specimens were more perpendicular to the direction
of force application than the square specimens. We are unsure what could have caused this
result. There is a possibility that it could be valid and be due to some characteristic of 3D printed
specimens, but based upon a force analysis it seems improbable, as the square cross­sections
would shear more easily than the angled layers.
As a result, in the future we would like to perform further bending tests on various specimens to
determine their elastic moduli, focusing on the pieces with square cross­sections. One of the
key methods of finding more accurate results in this area would be to create specimens with a
uniform cross­section, rather than the three different types used in these experiments. For the
test results above, the square specimen was the only one for which we used the linear
interpolation of the moment of inertia, and so this method would have been the source of this
discrepancy between the results and our hypothesis. Using specimens with the same cross
section would remove the need for scaling by moment of inertia, and so would yield a more
accurate value of the elastic modulus and yield stress for the square pieces. The other two
moment of inertia calculations required less approximate than the linear interpolation, and so we
considered them to be more valid results, but removing the need for moment of inertia
approximation would also improve those values as well.

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VII. Tension Test Results:
Our tension tests yielded graphs relating force and head displacement of the jaws, as shown in
Figure 24.
Figure 24: Force vs displacement data graphs.
Note: In this figure, each type of specimen responded to loading in the same way. The
vertical specimens both had a linear initial loading region and then the graphs bent at
around 500N of loading to another linear region. The angled specimens responded fairly
linearly to loading and the horizontal specimens both had a curved loading response.
Also note that these displacements are measured by the movement of the grips and so
includes stretching of the larger top and bottom region of the pieces or slipping of the
gripps. For future calculations we use the extensometer displacement because this
measured the elongation of the uniform cross­section in middle area of the pieces.
To analyze our data we looked at the force data and corresponding extensometer readings.
Since our tension specimens varied in fill density, the area by which we divided the force to get
stress varied between the pieces. For the young’s modulus, we approximated the
cross­sectional area of the thin center area as Adense (45mm2
) for the vertical pieces, Ashell
(39mm2
) for the horizontal pieces and Amedium (43mm2
) for the angled pieces, where Amedium was
a linear interpolation between the two other areas using the masses. These areas were chosen
because they corresponded to the cross sectional area of the center region ­ whose elongation
was measured using the extensometer.

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However, an additional problem with the tension specimens became apparent during testing.
Since the ends of the tension pieces were close to hollow (due to the lattice structure) it was
possible to crunch them too tight in the grips of the tension testing machine. This damaged the
structure of the piece, weakening it at that location, and creating a stress concentration at that
location. Thus, the pieces did not fail at the intended location, ie. in the middle of the part with
uniform cross­sectional area.
As a result, for the yield stress, we chose areas that reflected the cross sectional area at the
point of failure, where the yield began to occur, as shown in Figure 25. These areas were
approximated as Avertical = 89mm2
and Ahorizontal = Aangled = 89mm2
.
Figure 25: Break surfaces. Dashed red lines indicate initial failure plane
Print orientation: a) Horizontal, b) Vertical, c) Angled
Using these areas we found the stress from the force measurements and plotted Stress vs.
Strain curves to find the young’s modulus, as shown in Figure 26.

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Figure 26: Linear Regions of Stress vs. Strain plots.
Note: We assume the extensometer slipped for one for one of the vertical pieces because the
extensometer read negative values for most of the test and is therefore not included on the
vertical specimens graph.
The young’s modulus acquired from these graphs and the yield stress found from the three yield
“planes” of our three different specimen orientations are as follows:
Beam Orientation E (GPa) σy (MPa)
Horizontal 2.84 25.7
Angled 2.97 9.9
Vertical 3.16 5.45
VIII. Tension Test Analysis:
As we hypothesized, the horizontally printed pieces were the strongest of the tension specimens
in terms of the yield stress, with the angled samples being the second strongest and the vertical
pieces being the weakest.
Initially, we found it odd that the elastic modulus was the greatest for the vertical piece but on
further consideration this fits with the properties that arise from the process of 3D printing. This
result implies that for the same force the vertical pieces will elongate less, and therefore that the
interface between the layers is stiffer than the layers of printed material. Ultimately, though the
interface between the layers is not as able to withstand stresses as the printed material (is less
tough), and so exhibits a lower yield stress.
The results of our tension tests must be taken with a grain of salt however. Unanticipated fill
density complications made our specimens into structures significantly more complex than our

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intended sample structures. This necessitated that we scale the values achieved directly, by the
cross­sectional areas of the specimens in order to achieve the values of yield stress and
young’s modulus tabulated above. These areas were gross approximations and could have
severely affected the values found for the young’s modulus and yield stress of our specimens,
and therefore our interpretations of which specimens appeared stronger than others.
VII. Future tests:
The key direction in which we would like to extend our experimentation in this field is by removing
the need for much of the data processing that we performed. The key difficulty that we
experienced in both our bending and tension tests, primarily with our tension tests, was the fact
that the printed pieces had a variety of internal structures, as opposed to a single type. This
required us to perform a series of approximations of moments of inertia for bending and areas
for tension tests, which in the case of our tension tests was often a gross approximation.
Additionally, the variety of internal densities in the tension specimens resulted in the pieces failing
at the transitional point between the part of the piece gripped by the jaws and the region in which
it was supposed to fail.
There are a number of ways in which we can rectify the problems that we experienced with the
varying internal densities of the specimens. One method would be to specify the parts to be
printed as shells, with no internal lattice­work so that the only difference between the specimens
would arise from the print orientations. If the print orientations resulted in a different wall
thickness, scaling by this area is much more predictable, and therefore accurate, than
estimating the cross­sectional area of a lattice or the moment of inertia of a specimen containing
a lattice.
A second method of testing that would ameliorate this problem would be to print solid
specimens, which would have a similar effect to printing hollow specimens. Printing solid
specimens of the same dimensions as the samples used in these tests would not be
economical, due to the high price of 3D printing, and so we could instead use flat specimens that
are rectangular in shape. A further advantage of the solid specimens would be that they would
remove the problem of the jaws crushing the tension specimens and creating a stress
concentration factor at the point of contact, which was the likely cause of the pieces failing along
the jaws.
Yet another way that we could potentially generate more accurate values for the material
properties of the parts by performing a compression test rather than a tension test. The
compression specimens would not require parts able to be gripped by the vise, and so would
prevent a change in the internal density of the specimen. Both a young’s modulus and a
compressive yield stress could be generated for these tests as well. Additionally, the
compression samples would have the benefit of being less expensive and faster to print due to
the less complicated geometry.

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One final test that we would like to perform in the future is to vary the angle of the angled bending
specimens from 45 degrees. We would expect that varying the angle of both the specimens with
the angle visible on the top of the piece and on the side would cause them to approach the
behavior of either the horizontal, vertical, or square specimens. Varying the angle of the angled
side specimens, would equate to progressing from the horizontal specimen to the square
specimen, and varying the angle of the angled top specimens would equate to progressing from
the vertical specimens to the square specimens. It would be interesting to discover if the
specimens do exhibit this behavior, and then to graphically relate the angle between the layers
with the yield force and young’s modulus for this variety of angles.
VIII. Conclusion:
Samples created using Fused Deposition Modeling contain different internal geometries based
upon the direction in which the layers of plastic were constructed. Each of the tests that we
performed was designed to give us insight into how these 3D printed specimens behaved when
subjected to tension or bending forces when they were oriented differently. For each test, we
found the yield stress and the young’s modulus, and used these material properties to compare
the performance of each type of orientation. Overall, we found that the bending tests validated
our hypothesis that the more perpendicular the layers are to the direction of force application, the
higher the yield stress was. The relative values of the young’s also followed this trend, with the
exception of the specimens we termed “square”. This exception is not one we can satisfactorily
explain, and so would be one of the subjects of future testing. For the tension specimens,
several problems arose as a result of unanticipated variations in internal density caused by the
deposition machine. However, the relative values of the yield stress validated what we expected
in that the parallel the layers were to the direction of force application, the higher the yield stress.
In the case of the young’s modulus on the other hand, we found that the more perpendicular the
layers were to the direction of force application the higher the young’s modulus was. Future
experimentation in this field would likely focus on testing specimens with uniform internal
structure in order to yield more accurate results for both bending and tension tests by removing
the need for approximations in the processing of the data.